There has conventionally been known a tire pressure monitoring system having a tire pressure monitor provided on a vehicle body for notifying a driver of a trouble in tire pressure, and a sensor unit installed in a tire wheel of the vehicle for sensing pressure of a tire and transmitting information about the sensed tire pressure to the tire pressure monitor via radio waves.
There has also been proposed a system in which, in order to notify the driver of information about a mounting position in the vehicle of the sensor unit detecting a trouble of the tire, for example, the right front wheel of the vehicle as well as the tire pressure in case of detecting a trouble in tire pressure, a self-identification code specific for each sensor unit is stored in a fixing memory of the sensor unit at each mounting position and a corresponding relation between each sensor unit and mounting position in the vehicle is set and stored in the tire pressure monitor beforehand, so that, when the sensor unit detect a trouble, the sensor unit transmits the self-identification code as well as the information about tire pressure to the tire pressure monitor while the tire pressure monitor specify the corresponding mounting position in the vehicle based on the transmitted self-identification code to notify the driver of the position.
In this conventional system, the self-identification code of the sensor unit is usually configured to be written in its fixing memory during the manufacturing of the sensor unit and unable to be rewritten after shipment to prevent the data from rewriting by a malfunction or the like.
The above-mentioned operation of setting the corresponding relation between the self-identification code and the mounting position in the vehicle of the sensor unit is usually performed during the manufacturing stage of the vehicle prior to the shipment. The operation is performed by, for example, actually reducing each tire pressure to tentatively cause a trouble, subsequently recovering the tire pressure, associating the transmitted self-identification code with the position in the vehicle of the tire, storing the association in the tire pressure monitor, and repeating this sequence, which operation is extremely complex.
The conventional tire pressure sensor unit has the following problems. That is, when any one of sensor units in the respective mounting position in the vehicle is replaced with a new unit due to a breakdown or the like, the replacing sensor unit has a different self-identification code from that of the sensor unit having been installed before the replacement, so that an operation of setting a relation between the new self-identification code and a mounting position in the vehicle of the sensor unit has to be further performed, which is extremely complex and time consuming.
Moreover, when a replacement between summer tires and winter tires is conducted, the summer tires and the winter tires both of which are attached in a certain mounting position in the vehicle have respectively different self-identification code since these tires are stored and replaced in such a state that they are assembled in rims, so that an operation of associating the self-identification code with the mounting position in the vehicle of the tire pressure sensor unit is needed in every replacement between the summer tires and the winter tires. Due to the necessity of the time consuming operation, it is an actual condition that no tire pressure monitoring system notifying a mounting position in the vehicle of tire with which a trouble is detected has been made for practical use yet.
The present invention has been made in view of these problems, and its object is to provide a sensor unit capable of eliminating the operation of associating the self-identification number with the tire wheel to which the sensor unit is attached and facilitating a replacement operation of tire wheels when the tire wheel is replaced.